Method of drying articles being surface-coated

ABSTRACT

Wooden articles, to which a film of material like paint, lacquer and putty is applied, are repeatedly subjected to periods of surface heating at temperatures between 100* to 300* C. Between successive heating periods the articles are maintained in an atmosphere below 50*C. The surface heating periods are relatively short and between 5 and 15 seconds long to promote heating of the film in its entirety without heating the wood to an elevated temperature which is detrimental.

United States Patent Fagerstrom 1 July 25, 1972 METHOD OF DRYING ARTICLES [56] References Cited UNITED STATES PATENTS 3,405,020 10/1968 Chavannes ..1 17/] 19.8 3,364,062 l/1968 Mitchell... 2,758,386 8/1956 Cobb ..34/31 Primary Examiner-Carroll B. Dority, Jr. Att0rney-Edmund A. Fenander [57] ABSTRACT Wooden articles, to which a film of material like paint, lacquer and putty is applied, are repeatedly subjected to periods of surface heating at temperatures between 100 to 300C. Between successive heating periods the articles are maintained in an atmosphere below 50C. The surface heating periods are relatively short and between 5 and 15 seconds long to promote heating of the film in its entirety without heating the wood to an elevated temperature which is detrimental.

4 Claims, 3 Drawing Figures rimmed:

ill

METHOD OF DRYING ARTICLES BEING SURFACE- COATED The present invention relates to a method of heat treating articles, particularly wooden products, after or in connection with surface treating or coating with paint, lacquer, putty or the like. In industrial production of surface-treated articles a surface coating, film, of paint, lacquer, putty or the like is applied on the article in question which is then subjected to heat treatment for curing and drying of the film applied. To achieve a fully satisfactory result it is considered necessary to heat the articles to temperatures between 40 and 100C during a relatively long time, which may amount to half an hour or an hour. Temperature and time are chosen with respect to the articles treated. It has namely turned out, when treatment is effected at the temperatures indicated above, that the film applied will not be appropriate until after the times mentioned. Although the time can be shortened when the higher temperatures are used it has nevertheless been considered impossible to proceed in such manner because the surfacetreated articles will then be damaged by the high temperature. For instance, there are articles with glued-on details, such as glued edgings, and it has turned out to be very difficult to avoid damages in the glue joints during the treatment. It has even turned out that treatment at lower temperature and during longer time involves difficulties of the same kind because the articles are then heated throughout. In the case of wooden details, the base material is subjected to rising of the wood fibers, resin is precipitated and in some cases cracks appear. To these difficulties should be added the essential drawback in the known method that the conveyor-belt treatment during a long time for each detail calls for a plant of great length if it is desired to obtain an acceptable quantity of ready articles per unit of time in a plant. This involves a high cost not only for the treating plant proper but also for the premises in which it is placed.

The object of the present invention is on the one a to reduce the said difficulties in attaining a good result and on the other hand to eliminate the drawbacks of the high production cost. This is achieved by applying the invention which is characterized in that the articles are repeatedly subjected to periods of surface-heating within the temperature zone of 100-300 C. Between successive heating periods the articles are maintained in an atmosphere below 50C. The surface heating periods are relatively short and between and seconds long to promote heating of the film in its entirety without raising the temperature of the base material to an detrimental value.

A plant for carrying out the method is essentially characterized by a conveyor system for the articles which passes through one or several heating zones separated from each other and with temperatures between 100 and 300C.

The invention will be described below in connection with a surface-treating plant shown diagrammatically in the attached drawings.

FIG. i is a side view of a surface-treating plant;

FIG. 2 is a top plan view of the plant shown in FIG. H; and

FIG. 3 is a fragmentary view illustrating section III of FIG. 1 on an enlarged scale.

Through the surface treating plant of FIGS. 1 and 2 passes a conveyor 10, which can be made in a manner well known and preferably is provided with speed control. Due to its comparatively great length, the conveyor comprises suitably a number of parts connected with each other. The articles to be treated are introduced into the plant from the left in the Figures and are brought to an oven 11 in which they are preheated. Thereafter, the articles pass into a spraying chamber 12 in which a surface coating of paint, lacquer, putty or the like is applied. The surface coating can be applied in any well known manner by curtain-coating, spraying, dipping and spreading, for example. Thereafter the articles pass into an oven 13 with low heat in which air is vented and the applied coating is set. Upon this follows a drying oven 14, which also operates at a low temperature, for instance below 60C. Such an oven may often be dispensed with. The drying oven 14 is followed by a number of high temperature ovens l5, l6, l7, l8, 19. In these ovens, a temperature between and 300C is maintained, preferably about l50-225C. Each oven has such a short length in the direction of the conveyor that the stay of the articles in each oven will be short and preferably between 5 and 15 sec. depending on the speed of the conveyor belt. In some cases also a shorter or a somewhat longer time may preferably be used. Thus, the initial heating period can be longer than subsequent heating periods. By the arrangement of the ovens 15-19 at a certain distance from each other, the articles between two subsequent treatments will for some time be in an atmosphere below 50C which can be a temperature near that of the ambient air. If considered suitable, a vent hood with a suction fan can be arranged over that part of the plant which comprises the oven H549. Likewise, some air can be blown between the heating ovens in order to reduce the length of the stabilizing paths.

When the articles have been treated in the ovens 5-l9 they pass into a cooling zone 20 where cooling by air is effected. The articles finally pass through a surface-finishing machine 21. After that the articles move further to be piled for storing or transportation. It is also possible to arrange a similar plant parallel to the one shown but with a conveyor running in the opposite direction and to carry out for instance the base coating in the first plant and then transfer the articles to the second plant in which the covering coating is perfonned. If the premises allow it, these production lines can lie in a row to avoid sideways transports.

As appears from FIGS. 1 and 2, the distance between the two high temperature ovens l5 and 16 is less than the distance for instance between the two last high temperature ovens 18, 19 in the row. These distances are adapted in a suitable manner on the one hand in order to achieve the desired result of the treatment and on the other hand to limit the length of the plant as much as possible, in order to save costs for the space required and for equipment, as well as in order to thereby reduce the total transit time and increase the production per unit of time. As appears from FIG. 3, the ovens 15, i6, and H7, for example, can be provided with rollers 22 so that each oven without difficulty can be moved on the base 23 in the direction of the conveyor 10 and to a suitable position with the purpose of obtaining intervals suitable with respect to the articles to be treated, to the kind of surface coating applied on the articles and to the temperature at which the plant is to operate. It is desirable for the interval of time between successive heating periods to be of such length that the temperature of all parts of the film will be equalized. FUrther, the interval of time between successive surface heating periods can be adjusted so that it increases and becomes longer with repeated periods of surface heating of the articles. Also the speed of the conveyor affects the location of the ovens.

I claim:

1. In a method of heat treating wooden articles substantially at the time a film of material is applied to surfaces thereof which is selected from a group consisting of paint, lacquer and putty, the improvement which comprises the steps of repeatedly subjecting the wooden articles to periods of surface heating at temperatures between 100 to 300C. and, between successive surface heating periods, maintaining the wooden articles in an atmosphere which is below 50C. for a period of time necessary to maintain the temperature of the wood below a predetermined temperature, the surface heating periods being relatively short and between 5 and 15 seconds long to promote heating of the film in its entirety without heating the wood to an elevated temperature which is detrimental.

2. The improvement set forth in claim 1 in which the interval of time between successive heating periods is of such length that the temperature of all parts of the film will be equalized.

3. The improvement set forth in claim l in which the interval of time between successive surface heating periods increases with repeated periods of surface heating of the articles.

4. The improvement set forth in claim l in which the initial heating period is longer than subsequent heating periods. 

1. In a method of heat treating wooden articles substantially at the time a film of material is applied to surfaces thereof which is selected from a group consisting of paint, lacquer and putty, the improvement which comprises the steps of repeatedly subjecting the wooden articles to periods of surface heating at temperatures between 100* to 300*C. and, between successive surface heating periods, maintaining the wooden articles in an atmosphere which is below 50*C. for a period of time necessary to maintain the temperature of the wood below a predetermined temperature, the surface heating periods being relatively short and between 5 and 15 seconds long to promote heating of the film in its entirety without heating the wood to an elevated temperature which is detrimental.
 2. The improvement set forth in claim 1 in which the interval of time between successive heating periods is of such length that the temperature of all parts of the film will be equalized.
 3. The improvement set forth in claim 1 in which the interval of time between successive surface heating periods increases with repeated periods of surface heating of the articles.
 4. The improvement set forth in claim 1 in which the initial heating period is longer than subsequent heating periods. 